The present invention relates to sliding type constant velocity universal joints for use in power transmission mechanisms, for example, in automobiles and various kinds of industrial machines that allow axial displacement and angular displacement between two axes on the driving side and the driven side.
A power transmission mechanism that transmits power from the engine of an automobile to a drive wheel must respond to angular displacement and axial displacement based on changes in the relative positional relation between the engine and the wheel. Therefore, for example as shown in FIG. 21, an intermediate shaft 1 is interposed between the engine side and the drive wheel side, one end of the intermediate shaft 1 is coupled to a differential 3 through a sliding type constant velocity universal joint 2, and the other end thereof is coupled to the drive wheel 6 through a fixed type constant velocity universal joint 4 and a wheel bearing 5.
In the sliding type constant velocity universal joint 2 described above, not only angular displacement but also axial displacement is absorbed by so-called plunging, while in the fixed type constant velocity universal joint 4, only the angular displacement can be absorbed. The sliding type constant velocity universal joint 2, the fixed type constant velocity universal joint 4, and the intermediate shaft 1 constitute a drive shaft 7 as a unit, and as the drive shaft 7 is mounted in the vehicle body, the constant velocity universal joints 2 and 4 are set at prescribed operation angles. The operation angles of the constant velocity universal joints 2 and 4 sequentially change, and therefore, in general, among these joints 2 and 4, the fixed type constant velocity universal joint 4 is used on the outboard side and the sliding type constant velocity universal joint 2 is used on the inboard side to respond to the changing operation angles.
A double offset type constant velocity universal joint (DOJ) is well known as the sliding type constant velocity universal joint 2. As shown in FIGS. 22a and 22b, the constant velocity universal joint includes, as essential elements, a joint outer ring 8 attached to a differential 3 on the vehicle body side, a joint inner ring 9 attached to one end of the intermediate shaft 1, a plurality of balls 10 incorporated between the joint outer ring 8 and the joint inner ring 9, and a cage 11 interposed between the joint outer ring 8 and the joint inner ring 9 to support the balls 10. Note that a lid 16 to cover the opening is provided at the end of the joint outer ring 8 on the differential side.
The joint outer ring 8 is in the shape of a cup having a plurality of linear track grooves 12 parallel to its axial line and in its inner circumference at equal intervals in its circumferential direction. A plurality of linear track grooves 13 parallel to its axial line and corresponding to the track grooves 12 are provided in the outer circumference of the joint inner ring 9. The track grooves 12 and 13 in the joint outer ring 8 and the joint inner ring 9 cooperate with each other to define ball tracks in which the balls 10 transmitting torque are provided. The balls 10 are supported in the cage 11 interposed between the joint outer ring 8 and the joint inner ring 9. In the constant velocity universal joint, when an operation angle is set between the joint outer ring 8 and the joint inner ring 9, the cage 11 controls the balls 10 to be on the bisector plane of the operation angle so that the constant velocity is maintained.
Various types of rings may be used for the joint outer ring 8 in the constant velocity universal joint 2 depending on how the joint is attached to the vehicle body, and the one shown in FIGS. 22a and 22b is of flange type. The flange type joint outer ring 8 has protruding vehicle body attachment flanges 14 integrally formed at equal intervals in the circumferential direction at the outer circumferential end, and is attached to the differential 3 (see FIG. 21) by fastening bolts using the bolt holes 15 formed through the flanges 14. In the field of constant velocity universal joints, products having a joint outer ring 8 with a flower outer circumferential shape formed corresponding to the inner circumferential shape have been used in order to meet recent demands for lightweight and compact products (see for example, Japanese Patent Laid-Open Application No. Hei 5-231436).
The constant velocity universal joint having the flange type joint outer ring 8 has the plurality of vehicle body attachment flanges 14 protruding radially outwardly at the outer circumference of the joint outer ring 8 as described above, and the bolts are inserted through the bolt holes 15 in the vehicle body attachment flanges 14 for attachment to the differential on the vehicle body side.
As shown in FIGS. 23a and 23b, when the bolts are fastened to attach the joint outer ring 8, a fastening tool (socket 18 as shown) is used, and therefore there should be a space a from the outer circumference of the joint outer ring 8 for inserting the tool. Therefore, in consideration of the attaching process using the fastening tool, the necessity of providing the space a from the outer side of the joint outer ring 8 and the bolt holes 15 in the flanges 14 causes the outer diameter size of the vehicle body attachment flanges 14 to increase, which increases the weight of the constant velocity universal joint.
In the constant velocity universal joint, the number of balls 10 is typically six or eight, and the balls 10 are normally arranged in the circumferential direction at six equal pitch intervals (60°) or eight equal pitch intervals (45°). In this constant velocity universal joint, as shown in FIG. 23b, the balls 10 are provided at equal pitch intervals of 60°. If the number of the balls is not six or eight, the balls are arranged at equal pitch intervals in the circumferential direction.
In the constant velocity universal joint of this kind, when the torque is loaded and rotation is carried out, in other words, when power is transmitted, thrust force is induced in the axial direction of the constant velocity universal joint (induced thrust force), and the induced thrust force changes as many times as the number of the track grooves in one rotation. In the conventional constant velocity universal joint, the track grooves are arranged at equal intervals of 60°, and therefore the number of vibration frequency is six, which sometimes causes unnerving vibrations or muffled noises in resonance with the natural vibration frequency of the underbody of the vehicle.